• Step 1: In a large skillet or wok, heat the olive oil over medium-high heat. Add the beef and cook, stirring frequently, until browned and cooked through, about 5-7 minutes. Remove the beef from the pan and set aside.
• Step 2: Add the green beans to the same pan and cook, stirring occasionally, until crisp-tender, about 5 minutes.
• Step 3: Add the garlic and onion to the pan and cook for 2-3 minutes, until fragrant and the onion is translucent.
• Step 4: Return the cooked beef to the pan and add the soy sauce, rice vinegar, sesame oil, and red pepper flakes (if using). Stir to combine and cook for an additional 2-3 minutes, until the sauce has thickened slightly.
• Step 5: Season with salt and pepper to taste.